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- SUBJECTS AND METHODS
Primary Sjögren's syndrome (primary SS) is a chronic, inflammatory, autoimmune disease of unknown etiology (1). Prevalence figures reported in the literature vary due to the fact that different classification criteria are used. According to the Copenhagen criteria (2), which require 2 abnormal objective test results for dry eyes and dry mouth, respectively, the prevalence of SS was 2.7% in a population study in Sweden for the age group 52–72 years (3). In a community-based study of adults aged 18–75 years in the United Kingdom, the prevalence of primary SS (autoimmune and nonautoimmune) was estimated to be 3.3% (4) using the European Community (EC) criteria (5). The EC criteria include 6 items (2 symptoms and 4 objective tests), and the diagnosis is based on the presence of at least 4 of them. The peak incidence is between 40 and 60 years and the occurrence in women is about 9 times that of men (1).
Primary SS is characterized by hypofunction of the exocrine glands, especially the lacrimal and salivary glands, which result in the key symptoms, namely, dry eyes and dry mouth (1). Nonexocrine symptoms, such as disabling fatigue, arthralgia, myalgia, and mental symptoms, are other common complaints of primary SS (4, 6–8).
Impaired physical capacity, including decreased aerobic capacity, joint mobility, and muscle function, is a common consequence of many rheumatic disorders, such as rheumatoid arthritis (RA) (9, 10), systemic lupus erythematosus (SLE) (11–13), and fibromyalgia (FMS) (14, 15). The documentation on physical capacity in primary SS is sparse. In 2 recent studies concerning functional disability and health-related quality of life in primary SS (16, 17), patients reported that they experienced impaired physical function, i.e., activities such as vacuuming, going up stairs, walking, bathing, and dressing. To the best of our knowledge, no studies have reported measurements of physical capacity based on clinical examinations in primary SS.
The primary aim of this controlled, cross-sectional study was to describe aerobic capacity, muscle function, standing balance, and joint mobility in women with primary SS, and to compare the results with those of a control group matched for age and sex. A second aim was to investigate whether aerobic capacity correlates with experienced fatigue, functional disability, and mental aspects.
- Top of page
- SUBJECTS AND METHODS
This descriptive study presents information on physical capacity in women with primary SS based on clinical examinations and questionnaires. The results revealed small to moderate, significant reductions in aerobic capacity, joint mobility in the upper extremities, muscle function, and standing balance in women with primary SS compared with an age- and sex-matched control group from the general population.
The primary SS patients included in the present study fulfilled the EC criteria (5) for the diagnosis and had anti-SSA/SSB antibodies and/or autoimmune sialadenitis. At the time of investigation, they represented all available women at our clinic with autoimmune abnormality and fulfilling the eligibility criteria for this study. This reduces the selection bias as far as possible. A further strength is the representativness of our strict age- and sex-matched control group in relation to the general population. This is supported by the fact that weight and height are in concordance with the values for women aged 45–49 years previously tested for physical capacity in a study including 733 Swedish women (38).
Aerobic capacity was calculated by Åstrand's method (19), which is based on submaximal aerobic work. Submaximal tests are often used to predict maximal oxygen uptake when a maximal test is not possible or appropriate. The level of oxygen uptake was 11% less in the women with primary SS compared with the control group. According to the results of a Swedish investigation of aerobic capacity of 640 Swedish women from the general population (38), this decrease in aerobic capacity in the women with primary SS corresponds to an age difference of 10 years, i.e., from 40–45 years and 50–55 years, in Swedish women from the general population. The values of oxygen uptake reported for the women with primary SS of this study are higher than the values reported for 67 patients (24 men and 43 women) with RA of low to moderate disease activity and a mean (range) age of 53 (23–65) years (10), and 31 female patients with SLE without active disease in major organs with a median (range) age of 42 (25–51) years (13). In addition to having a reduced oxygen uptake, the women with primary SS in our study also experienced having to make a greater effort than the control group when performing the bicycle test, according to the RPE scale. Assuming that selection bias does not invalidate comparison between these studies, our data suggests that the patients with SS had an aerobic capacity that is intermediate to that in healthy people and patients with RA or SLE.
Both groups showed good shoulder arm mobility, close to normal values. However, there was a small (1 scale point) but significant difference between the groups. A decrease of 1 scale point means a small difference in mobility. However, the primary SS group more frequently experienced shoulder pain and rated the pain as more severe during the test, which might limit function when performing repetitive tasks.
The women with primary SS had a significantly lower strength and endurance of the knee flexors than the control subjects. A possible explanation of this could be the higher level of physical activity reported by the women in the control group, who to a greater extent participated in such activities as aerobics, bicycle exercise, and jogging, which ought to improve muscular strength and endurance in the lower limbs. Another explanation could be the lower level of aerobic capacity in the primary SS group because muscular endurance is dependent on oxygen uptake (39), which is also supported in our study, as there was a correlation between muscular endurance and aerobic capacity (data not shown). Maximal grip strength and mean strength for 10 seconds were also decreased in the primary SS group. Compared with the control group, both the peak and mean strength were reduced by approximately 20%. The values for the control subjects were similar to those published as normal values for women aged 40–49 (26). The hand arthralgia reported by the primary SS women might be one explanation for the reduced grip strength in this group. The decrease in standing balance for the primary SS compared with the control subjects was 11%. The mean value of the control group corresponded to the mean value of 153 male and female volunteers described in a study by Bohannon et al (25).
The women with primary SS were found to experience a slight reduction in physical ability as compared with the women in the control group. The median HAQ score was 0.13, which indicates a mild degree of limitation. As many as 45% had no problem in performing any of the activities included in the HAQ. One reason for the disability experienced could be the hand arthralgia and the reduced grip strength, because 5 of the 8 items of HAQ emphasize hand function and grip strength, and the HAQ score correlated (r = 0.68, P < 0.01). The median HAQ score (0.13) of the women with primary SS in our study is lower than that in SLE according to a study by Hochberg and Sutton (11). They reported a median HAQ score of 0.45 for 106 outpatients with SLE and a mean age of 41 years. Our values suggest that the disability in primary SS is intermediate between healthy controls and SLE patients.
The levels of anxiety and depression recorded for the primary SS patients in this study correspond to those of a recent Swedish study concerning anxiety and depression in primary SS (8). This study, by Valtýsdóttir et al, demonstrated significantly higher values for anxiety and depression in 67 primary SS patients (mean age 58, range 28–85 years) compared with a healthy control group (63 controls; mean age 57, range 54–60 years) as well as to a group of 38 RA patients (mean age 60, range 54–60 years).
Fatigue in primary SS is a symptom frequently reported (4, 6, 7) and the difference in fatigue between the groups of our study was expected and in accordance with results recently obtained by Barendregt et al (40). In our study, functional disability, depression, age, and aerobic capacity were possible explanations of experienced fatigue as measured by a modified Swedish version of CFS. A targeted program for physical activity, including aerobic training, would perhaps reduce fatigue. Such an effect is indicated for SLE patients in studies by Robb-Nicholson et al (41) and Daltroy et al (42), who reported that exercise resulted in an improved aerobic capacity and decreased fatigue. Disturbed sleeping habits in primary SS (43) was not evaluated in the present study.
Confounders, such as smoking and medication, could possibly influence our results. There was, however, no significant difference demonstrated between the primary SS group and the control group with respect to medication. On the other hand, there were significantly more smokers in the control group. In spite of this, the control group showed a higher oxygen uptake.
The women with primary SS participating in this study showed an impaired aerobic capacity, muscle strength and endurance in the flexors of the knee, standing balance, and joint mobility of the upper extremity compared with an age- and sex-matched reference group. There was a correlation between aerobic capacity and experienced fatigue. Whether or not a training program including exercises for flexibility, muscle strength, standing balance, and aerobic exercises would improve physical capacity and reduce fatigue remains to be investigated.